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Abstract:

A cutting element for a drill bit that includes an outer support element
having at least a bottom portion and a side portion; and an inner
rotatable cutting element, a portion of which is disposed in the outer
support element, wherein the inner rotatable cutting element includes a
substrate and a diamond cutting face having a thickness of at least 0.050
inches disposed on an upper surface of the substrate; and wherein a
distance from an upper surface of the diamond cutting face to a bearing
surface between the inner rotatable cutting element and the outer support
element ranges from 0 to about 0.300 inches is disclosed.

Claims:

1.-54. (canceled)

55. A cutting structure for a cutting tool, comprising: an outer support
element having a bottom portion and a side portion; and an inner
rotatable cutting element, a portion of which is disposed in the outer
support element; wherein the outer support element further comprises an
inner shaft portion extending from the bottom portion into the inner
rotatable cutting element.

56. The cutting structure of claim 55, wherein the inner shaft portion is
threadedly attached to the bottom portion.

57. The cutting structure of claim 55, wherein the inner shaft portion is
integral with the bottom portion.

58. The cutting structure of claim 55, wherein an upper end of the inner
shaft portion extends partially over a cutting face of the inner
rotatable cutting element.

59. The cutting structure of claim 55, wherein at least a portion of a
bearing surface of the outer support element comprises a lubricious
material.

60. The cutting structure of claim 55, wherein the outer support element
is integral with a cutting tool body.

61. The cutting structure of claim 55, wherein at least a side portion of
the outer support element is a blade of a cutting tool.

62. The cutting structure of claim 55, wherein the outer support element
is a discrete element.

63. The cutting structure of claim 55, wherein a plurality of surface
alterations are formed in at least one of a working surface of the inner
rotatable cutting element, a substrate surface of the inner rotatable
cutting element, and an inner hole of the inner rotatable cutting
element.

64. The cutting structure of claim 63, wherein the surface alterations
have a depth ranging from 0.001 to 0.05 inches.

65. A cutting structure for a cutting tool, comprising: an outer support
element comprising a bottom portion and a side portion; an inner
rotatable cutting element, a portion of which is disposed in the outer
support element, wherein the inner rotatable cutting element comprises: a
substrate; a cutting face disposed on an upper surface of the substrate;
and a groove formed in a side surface of the substrate; and a retention
mechanism, wherein the retention mechanism extends radially inward from
the side portion of the outer support element into the groove.

67. The cutting structure of claim 65, wherein the retention mechanism
comprises a protrusion formed on the side portion of the outer support
element.

68. The cutting structure of claim 65, wherein the retention mechanism is
integral with the outer support element.

69. The cutting structure of claim 65, wherein at least a portion of the
outer support element is integral with the cutting tool.

70. The cutting structure of claim 65, wherein at least a portion of a
bearing surface of the cutter pocket comprises a lubricious material.

71. The cutting structure of claim 65, wherein a plurality of surface
alterations are formed in a surface of the inner rotatable cutting
element.

72. The cutting structure of claim 65, wherein the outer support element
comprises a second groove in an inner surface of the side portion of the
outer support element substantially matching the groove formed in the
side surface of the substrate, and wherein the retention mechanism
comprises at least one retention ball disposed within a space defined by
the groove formed in a side surface of the substrate and the second
groove.

73. A cutting structure for a cutting tool, comprising: an outer support
element; and an inner rotatable cutting element, a portion of which is
disposed in the outer support element, wherein the inner rotatable
cutting element comprises a substantially planar diamond cutting face,
and wherein the diamond cutting face comprises a plurality of recesses
radially spaced around the entire circumferential edge of the inner
rotatable cutting element.

74. The cutting structure of claim 73, wherein the plurality of recesses
have a depth ranging from 0.001 to 0.050 inches.

75. The drill bit of claim 73, wherein the outer support element is
integral with a cutting tool body.

76. The cutting structure of claim 73, wherein at least a portion of a
bearing surface of the outer support element comprises a lubricious
material.

77. The cutting structure of claim 73, wherein the outer support element
comprises at least a top portion and a side portion.

78. The cutting structure of claim 73, wherein the outer support element
comprises at least a bottom portion and a side portion.

79. A cutting structure for a cutting tool, comprising: an outer support
element; and an inner rotatable cutting element, a portion of which is
disposed in the outer support element; wherein a sealing element is
disposed between the inner rotatable cutting element and the outer
support element.

80. The cutting structure of claim 79, wherein the sealing element
comprises a metal seal component and an o-ring component.

81. The cutting structure of claim 79, wherein at least a portion of a
bearing surface of the outer support element comprises a lubricious
material.

82. The cutting structure of claim 79, wherein the outer support element
comprises at least a top portion and side portion.

83. The cutting structure of claim 79, wherein the outer support element
comprises at least a side portion and a bottom portion.

84. A cutting structure for a cutting tool, comprising: an outer support
element comprising at least a bottom portion and a side portion; and an
inner rotatable cutting element, a portion of which is disposed in the
outer support element; wherein at least one ball bearing is disposed
between a lower surface of the inner rotatable cutting element and the
bottom portion of the outer support element.

85. The cutting structure of claim 84, wherein the outer support element
is integral with a cutting tool body.

86. The cutting structure of claim 84, wherein the outer support element
further comprises a top portion that covers at least a portion of an
upper surface of the inner rotatable cutting element.

87. The cutting structure of claim 84, wherein the inner rotatable
cutting element comprises a substrate and a diamond cutting face disposed
on an upper surface of the substrate.

88. The cutting structure of claim 84, wherein at least a portion of a
bearing surface comprises a lubricious material.

[0005] Drill bits used to drill wellbores through earth formations
generally are made within one of two broad categories of bit structures.
Drill bits in the first category are generally known as "roller cone"
bits, which include a bit body having one or more roller cones rotatably
mounted to the bit body. The bit body is typically formed from steel or
another high strength material. The roller cones are also typically
formed from steel or other high strength material and include a plurality
of cutting elements disposed at selected positions about the cones. The
cutting elements may be formed from the same base material as is the
cone. These bits are typically referred to as "milled tooth" bits. Other
roller cone bits include "insert" cutting elements that are press
(interference) fit into holes formed and/or machined into the roller
cones. The inserts may be formed from, for example, tungsten carbide,
natural or synthetic diamond, boron nitride, or any one or combination of
hard or superhard materials.

[0006] Drill bits of the second category are typically referred to as
"fixed cutter" or "drag" bits. This category of bits has no moving
elements but rather have a bit body formed from steel or another high
strength material and cutters (sometimes referred to as cutter elements,
cutting elements or inserts) attached at selected positions to the bit
body. For example, the cutters may be formed having a substrate or
support stud made of carbide, for example tungsten carbide, and an ultra
hard cutting surface layer or "table" made of a polycrystalline diamond
material or a polycrystalline boron nitride material deposited onto or
otherwise bonded to the substrate at an interface surface.

[0007] An example of a prior art drag bit having a plurality of cutters
with ultra hard working surfaces is shown in FIG. 1a. A drill bit 10
includes a bit body 12 and a plurality of blades 14 that are formed on
the bit body 12. The blades 14 are separated by channels or gaps 16 that
enable drilling fluid to flow between and both clean and cool the blades
14 and cutters 18. Cutters 18 are held in the blades 14 at predetermined
angular orientations and radial locations to present working surfaces 20
with a desired backrake angle against a formation to be drilled.
Typically, the working surfaces 20 are generally perpendicular to the
axis 19 and side surface 21 of a cylindrical cutter 18. Thus, the working
surface 20 and the side surface 21 meet or intersect to form a
circumferential cutting edge 22.

[0008] Nozzles 23 are typically formed in the drill bit body 12 and
positioned in the gaps 16 so that fluid can be pumped to discharge
drilling fluid in selected directions and at selected rates of flow
between the cutting blades 14 for lubricating and cooling the drill bit
10, the blades 14, and the cutters 18. The drilling fluid also cleans and
removes the cuttings as the drill bit rotates and penetrates the
geological formation. The gaps 16, which may be referred to as "fluid
courses," are positioned to provide additional flow channels for drilling
fluid and to provide a passage for formation cuttings to travel past the
drill bit 10 toward the surface of a wellbore (not shown).

[0009] The drill bit 10 includes a shank 24 and a crown 26. Shank 24 is
typically formed of steel or a matrix material and includes a threaded
pin 28 for attachment to a drill string. Crown 26 has a cutting face 30
and outer side surface 32. The particular materials used to form drill
bit bodies are selected to provide adequate toughness, while providing
good resistance to abrasive and erosive wear. For example, in the case
where an ultra hard cutter is to be used, the bit body 12 may be made
from powdered tungsten carbide (WC) infiltrated with a binder alloy
within a suitable mold form. In one manufacturing process the crown 26
includes a plurality of holes or pockets 34 that are sized and shaped to
receive a corresponding plurality of cutters 18.

[0010] The combined plurality of surfaces 20 of the cutters 18 effectively
forms the cutting face of the drill bit 10. Once the crown 26 is formed,
the cutters 18 are positioned in the pockets 34 and affixed by any
suitable method, such as brazing, adhesive, mechanical means such as
interference fit, or the like. The design depicted provides the pockets
34 inclined with respect to the surface of the crown 26. The pockets 34
are inclined such that cutters 18 are oriented with the working face 20
at a desired rake angle in the direction of rotation of the bit 10, so as
to enhance cutting. It should be understood that in an alternative
construction (not shown), the cutters may each be substantially
perpendicular to the surface of the crown, while an ultra hard surface is
affixed to a substrate at an angle on a cutter body or a stud so that a
desired rake angle is achieved at the working surface.

[0011] A typical cutter 18 is shown in FIG. 1b. The typical cutter 18 has
a cylindrical cemented carbide substrate body 38 having an end face or
upper surface 54 referred to herein as the "interface surface" 54. An
ultra hard material layer (cutting layer) 44, such as polycrystalline
diamond or polycrystalline cubic boron nitride layer, forms the working
surface 20 and the cutting edge 22. A bottom surface 52 of the ultra hard
material layer 44 is bonded on to the upper surface 54 of the substrate
38. The bottom surface 52 and the upper surface 54 are herein
collectively referred to as the interface 46. The top exposed surface or
working surface 20 of the cutting layer 44 is opposite the bottom surface
52. The cutting layer 44 typically has a flat or planar working surface
20, but may also have a curved exposed surface, that meets the side
surface 21 at a cutting edge 22.

[0012] Generally speaking, the process for making a cutter 18 employs a
body of tungsten carbide as the substrate 38. The carbide body is placed
adjacent to a layer of ultra hard material particles such as diamond or
cubic boron nitride particles and the combination is subjected to high
temperature at a pressure where the ultra hard material particles are
thermodynamically stable. This results in recrystallization and formation
of a polycrystalline ultra hard material layer, such as a polycrystalline
diamond or polycrystalline cubic boron nitride layer, directly onto the
upper surface 54 of the cemented tungsten carbide substrate 38.

[0013] One type of ultra hard working surface 20 for fixed cutter drill
bits is formed as described above with polycrystalline diamond on the
substrate of tungsten carbide, typically known as a polycrystalline
diamond compact (PDC), PDC cutters, PDC cutting elements, or PDC inserts.
Drill bits made using such PDC cutters 18 are known generally as PDC
bits. While the cutter or cutter insert 18 is typically formed using a
cylindrical tungsten carbide "blank" or substrate 38 which is
sufficiently long to act as a mounting stud 40, the substrate 38 may also
be an intermediate layer bonded at another interface to another metallic
mounting stud 40.

[0014] The ultra hard working surface 20 is formed of the polycrystalline
diamond material, in the form of a cutting layer 44 (sometimes referred
to as a "table") bonded to the substrate 38 at an interface 46. The top
of the ultra hard layer 44 provides a working surface 20 and the bottom
of the ultra hard layer cutting layer 44 is affixed to the tungsten
carbide substrate 38 at the interface 46. The substrate 38 or stud 40 is
brazed or otherwise bonded in a selected position on the crown of the
drill bit body 12 (FIG. 1a). As discussed above with reference to FIG.
1a, the PDC cutters 18 are typically held and brazed into pockets 34
formed in the drill bit body at predetermined positions for the purpose
of receiving the cutters 18 and presenting them to the geological
formation at a rake angle.

[0015] Bits 10 using conventional PDC cutters 18 are sometimes unable to
sustain a sufficiently low wear rate at the cutter temperatures generally
encountered while drilling in abrasive and hard rock. These temperatures
may affect the life of the bit 10, especially when the temperatures reach
700-750° C., resulting in structural failure of the ultra hard
layer 44 or PDC cutting layer. A PDC cutting layer includes individual
diamond "crystals" that are interconnected. The individual diamond
crystals thus form a lattice structure. A metal catalyst, such as cobalt
may be used to promote recrystallization of the diamond particles and
formation of the lattice structure. Thus, cobalt particles are typically
found within the interstitial spaces in the diamond lattice structure.
Cobalt has a significantly different coefficient of thermal expansion as
compared to diamond. Therefore, upon heating of a diamond table, the
cobalt and the diamond lattice will expand at different rates, causing
cracks to form in the lattice structure and resulting in deterioration of
the diamond table.

[0016] It has been found by applicants that many cutters 18 develop
cracking, spalling, chipping and partial fracturing of the ultra hard
material cutting layer 44 at a region of cutting layer subjected to the
highest loading during drilling. This region is referred to herein as the
"critical region" 56. The critical region 56 encompasses the portion of
the ultra hard material layer 44 that makes contact with the earth
formations during drilling. The critical region 56 is subjected to high
magnitude stresses from dynamic normal loading, and shear loadings
imposed on the ultra hard material layer 44 during drilling. Because the
cutters are typically inserted into a drag bit at a rake angle, the
critical region includes a portion of the ultra hard material layer near
and including a portion of the layer's circumferential edge 22 that makes
contact with the earth formations during drilling.

[0017] The high magnitude stresses at the critical region 56 alone or in
combination with other factors, such as residual thermal stresses, can
result in the initiation and growth of cracks 58 across the ultra hard
layer 44 of the cutter 18. Cracks of sufficient length may cause the
separation of a sufficiently large piece of ultra hard material,
rendering the cutter 18 ineffective or resulting in the failure of the
cutter 18. When this happens, drilling operations may have to be ceased
to allow for recovery of the drag bit and replacement of the ineffective
or failed cutter. The high stresses, particularly shear stresses, may
also result in delamination of the ultra hard layer 44 at the interface
46.

[0018] In some drag bits, PDC cutters 18 are fixed onto the surface of the
bit 10 such that a common cutting surface contacts the formation during
drilling. Over time and/or when drilling certain hard but not necessarily
highly abrasive rock formations, the edge 22 of the working surface 20
that constantly contacts the formation begins to wear down, forming a
local wear flat, or an area worn disproportionately to the remainder of
the cutting element. Local wear flats may result in longer drilling times
due to a reduced ability of the drill bit to effectively penetrate the
work material and a loss of rate of penetration caused by dulling of edge
of the cutting element. That is, the worn PDC cutter acts as a friction
bearing surface that generates heat, which accelerates the wear of the
PDC cutter and slows the penetration rate of the drill. Such flat
surfaces effectively stop or severely reduce the rate of formation
cutting because the conventional PDC cutters are not able to adequately
engage and efficiently remove the formation material from the area of
contact. Additionally, the cutters are typically under constant thermal
and mechanical load. As a result, heat builds up along the cutting
surface, and results in cutting element fracture. When a cutting element
breaks, the drilling operation may sustain a loss of rate of penetration,
and additional damage to other cutting elements, should the broken
cutting element contact a second cutting element.

[0019] Additionally, another factor in determining the longevity of PDC
cutters is the generation of heat at the cutter contact point,
specifically at the exposed part of the PDC layer caused by friction
between the PCD and the work material. This heat causes thermal damage to
the PCD in the form of cracks which lead to spalling of the
polycrystalline diamond layer, delamination between the polycrystalline
diamond and substrate, and back conversion of the diamond to graphite
causing rapid abrasive wear. The thermal operating range of conventional
PDC cutters is typically 750° C. or less.

[0020] In U.S. Pat. No. 4,553,615, a rotatable cutting element for a drag
bit was disclosed with an objective of increasing the lifespan of the
cutting elements and allowing for increased wear and cuttings removal.
The rotatable cutting elements disclosed in the '615 patent include a
thin layer of an agglomerate of diamond particles on a carbide backing
layer having a carbide spindle, which may be journalled in a bore in a
bit, optionally through an annular bush. With significant increases in
loads and rates of penetration, the cutting element of the '615 patent is
likely to fail by one of several failure modes. Firstly, thin layer of
diamond is prone to chipping and fast wearing. Secondly, geometry of the
cutting element would likely be unable to withstand heavy loads,
resulting in fracture of the element along the carbide spindle. Thirdly,
the retention of the rotatable portion is weak and may cause the
rotatable portion to fall out during drilling.

[0021] Accordingly, there exists a continuing need for cutting elements
that may stay cool and avoid the generation of local wear flats.

SUMMARY OF INVENTION

[0022] In one aspect, embodiments disclosed herein relate to a cutting
element for a drill bit that includes an outer support element having at
least a bottom portion and a side portion; and an inner rotatable cutting
element, a portion of which is disposed in the outer support element,
wherein the inner rotatable cutting element includes a substrate and a
diamond cutting face having a thickness of at least 0.050 inches disposed
on an upper surface of the substrate; and wherein a distance from an
upper surface of the diamond cutting face to a bearing surface between
the inner rotatable cutting element and the outer support element ranges
from 0 to about 0.300 inches.

[0023] In another aspect, embodiments disclosed herein relate to a cutting
element that includes an outer support element having at least a bottom
portion and a side portion; an inner rotatable cutting element, a portion
of which is disposed in the outer support element, wherein the inner
rotatable cutting element includes a substrate and a diamond cutting face
having a thickness of at least 0.050 inches disposed on an upper surface
of the substrate; and a retention mechanism for retaining the inner
rotatable cutting element in the outer support element.

[0024] In another aspect, embodiments disclosed herein relate to a cutting
element that includes an outer support element; and an inner rotatable
cutting element, a portion of which is disposed in the outer support
element, wherein the inner rotatable cutting element includes a substrate
and a diamond cutting face having a thickness of at least 0.050 inches
disposed on an upper surface of the substrate; and wherein a first
portion of the outer support element and the inner rotatable cutting
element comprise conical bearing surfaces therebetween.

[0025] In another aspect, embodiments disclosed herein relate to a cutting
element that includes an outer support element; and an inner rotatable
cutting element, a portion of which is disposed in the outer support
element, wherein the inner rotatable cutting element includes a substrate
and a diamond cutting face having a thickness of at least 0.050 inches
disposed on an upper surface of the substrate; and wherein the outer
support element and the inner rotatable cutting element comprise bearing
surfaces therebetween, wherein at least a portion of the bearing surfaces
comprise diamond particles.

[0026] In another aspect, embodiments disclosed herein relate to a cutting
element that includes an outer support element; and an inner rotatable
cutting portion, a portion of which is disposed in the outer support
element, wherein the inner rotatable cutting element includes a substrate
and a diamond cutting face having a thickness of at least 0.050 inches
disposed on an upper surface of the substrate; and wherein at least a
portion of the diamond cutting face is non-planar.

[0027] In yet another aspect, embodiments disclosed herein relate to a
cutting element that includes an outer support element; and an inner
rotatable cutting portion, a portion of which is disposed in the outer
support element, wherein the inner rotatable cutting element includes a
substrate and a diamond cutting face having a thickness of at least 0.050
inches disposed on an upper surface of the substrate; and wherein at
least a portion of the inner rotatable cutting element comprises surface
alterations.

[0028] Other aspects and advantages of the invention will be apparent from
the following description and the appended claims.

[0052] In one aspect, embodiments disclosed herein relate to rotatable
cutting structures for drill bits. Specifically, embodiments disclosed
herein relate to a cutting element that includes an inner rotatable
cutting element and an outer, static support element, wherein a portion
of the inner rotatable cutting element is surrounded by the outer support
element.

[0053] Generally, cutting elements described herein allow at least one
surface or portion of the cutting element to rotate as the cutting
elements contact a formation. As the cutting element contacts the
formation, the cutting action may allow portion of the cutting element to
rotate around a cutting element axis extending through the cutting
element. Rotation of a portion of the cutting structure may allow for a
cutting surface to cut the formation using the entire outer edge of the
cutting surface, rather than the same section of the outer edge, as
observed in a conventional cutting element.

[0054] The rotation of the inner rotatable cutting element may be
controlled by the side cutting force and the frictional force between the
bearing surfaces. If the side cutting force generates a torque which can
overcome the torque from the frictional force, the rotatable portion will
have rotating motion. The side cutting force may be affected by cutter
side rake, back rake and geometry, including the working surface patterns
disclosed herein. Additionally, the side cutting force may be affected by
the surface finishing of the surfaces of the cutting element components,
the frictional properties of the formation, as well as drilling
parameters, such as depth of cut. The frictional force at the bearing
surfaces may affected, for example, by surface finishing, mud intrusion,
etc. The design of the rotatable cutters disclosed herein may be selected
to ensure that the side cutting force overcomes the frictional force to
allow for rotation of the rotatable portion.

[0055] Referring to FIG. 2A-B, a cutting element in accordance with one
embodiment of the present disclosure is shown. As shown in this
embodiment, cutting element 200 includes an inner rotatable (dynamic)
cutting element 210 which is partially disposed in, and thus, partially
surrounded by an outer support (static) element 220. Outer support
element 220 includes a bottom portion 222 and a side portion 224. Inner
rotatable cutting element 210, partially disposed within the cavity
defined by the bottom portion 222 and side portion 224, includes a
cutting face 212 portion disposed on an upper surface of substrate 214.
Additionally, while bottom portion 222 and side portion 224 of the outer
support element 220 are shown in FIG. 2 as being integral, one of
ordinary skill in the art would appreciate that depending on the geometry
of the cutting element components, the bottom and side portions may
alternatively be two separate pieces bonded together. In yet another
embodiment, the outer support element 220 may be formed from two separate
pieces bonded together on a vertical plane (with respect to the cutting
element axis, for example) to surround at least a portion of the inner
rotatable cutting element 210.

[0056] In various embodiments, the cutting face of the inner rotatable
cutting element may include an ultra hard layer that may be comprised of
a polycrystalline diamond table, a thermally stable diamond layer (i.e.,
having a thermal stability greater than that of conventional
polycrystalline diamond, 750° C.), or other ultra hard layer such
as a cubic boron nitride layer.

[0057] As known in the art, thermally stable diamond may be formed in
various manners. A typical polycrystalline diamond layer includes
individual diamond "crystals" that are interconnected. The individual
diamond crystals thus form a lattice structure. A metal catalyst, such as
cobalt, may be used to promote recrystallization of the diamond particles
and formation of the lattice structure. Thus, cobalt particles are
typically found within the interstitial spaces in the diamond lattice
structure. Cobalt has a significantly different coefficient of thermal
expansion as compared to diamond. Therefore, upon heating of a diamond
table, the cobalt and the diamond lattice will expand at different rates,
causing cracks to form in the lattice structure and resulting in
deterioration of the diamond table.

[0058] To obviate this problem, strong acids may be used to "leach" the
cobalt from a polycrystalline diamond lattice structure (either a thin
volume or entire tablet) to at least reduce the damage experienced from
heating diamond-cobalt composite at different rates upon heating.
Examples of "leaching" processes can be found, for example, in U.S. Pat.
Nos. 4,288,248 and 4,104,344. Briefly, a strong acid, typically
hydrofluoric acid or combinations of several strong acids may be used to
treat the diamond table, removing at least a portion of the co-catalyst
from the PDC composite. Suitable acids include nitric acid, hydrofluoric
acid, hydrochloric acid, sulfuric acid, phosphoric acid, or perchloric
acid, or combinations of these acids. In addition, caustics, such as
sodium hydroxide and potassium hydroxide, have been used to the carbide
industry to digest metallic elements from carbide composites. In
addition, other acidic and basic leaching agents may be used as desired.
Those having ordinary skill in the art will appreciate that the molarity
of the leaching agent may be adjusted depending on the time desired to
leach, concerns about hazards, etc.

[0059] By leaching out the cobalt, thermally stable polycrystalline (TSP)
diamond may be formed. In certain embodiments, only a select portion of a
diamond composite is leached, in order to gain thermal stability without
losing impact resistance. As used herein, the term TSP includes both of
the above (i.e., partially and completely leached) compounds.
Interstitial volumes remaining after leaching may be reduced by either
furthering consolidation or by filling the volume with a secondary
material, such by processes known in the art and described in U.S. Pat.
No. 5,127,923, which is herein incorporated by reference in its entirety.

[0060] Alternatively, TSP may be formed by forming the diamond layer in a
press using a binder other than cobalt, one such as silicon, which has a
coefficient of thermal expansion more similar to that of diamond than
cobalt has. During the manufacturing process, a large portion, 80 to 100
volume percent, of the silicon reacts with the diamond lattice to form
silicon carbide which also has a thermal expansion similar to diamond.
Upon heating, any remaining silicon, silicon carbide, and the diamond
lattice will expand at more similar rates as compared to rates of
expansion for cobalt and diamond, resulting in a more thermally stable
layer. PDC cutters having a TSP cutting layer have relatively low wear
rates, even as cutter temperatures reach 1200° C. However, one of
ordinary skill in the art would recognize that a thermally stable diamond
layer may be formed by other methods known in the art, including, for
example, by altering processing conditions in the formation of the
diamond layer.

[0061] The substrate on which the cutting face is disposed may be formed
of a variety of hard or ultra hard particles. In one embodiment, the
substrate may be formed from a suitable material such as tungsten
carbide, tantalum carbide, or titanium carbide. Additionally, various
binding metals may be included in the substrate, such as cobalt, nickel,
iron, metal alloys, or mixtures thereof. In the substrate, the metal
carbide grains are supported within the metallic binder, such as cobalt.
Additionally, the substrate may be formed of a sintered tungsten carbide
composite structure. It is well known that various metal carbide
compositions and binders may be used, in addition to tungsten carbide and
cobalt. Thus, references to the use of tungsten carbide and cobalt are
for illustrative purposes only, and no limitation on the type substrate
or binder used is intended. In another embodiment, the substrate may also
be formed from a diamond ultra hard material such as polycrystalline
diamond and thermally stable diamond. While the illustrated embodiments
show the cutting face and substrate as two distinct pieces, one of skill
in the art should appreciate that it is within the scope of the present
disclosure the cutting face and substrate are integral, identical
compositions. In such an embodiment, it may be preferable to have a
single diamond composite forming the cutting face and substrate or
distinct layers.

[0062] The outer support element may be formed from a variety of
materials. In one embodiment, the outer support element may be formed of
a suitable material such as tungsten carbide, tantalum carbide, or
titanium carbide. Additionally, various binding metals may be included in
the outer support element, such as cobalt, nickel, iron, metal alloys, or
mixtures thereof, such that the metal carbide grains are supported within
the metallic binder. In a particular embodiment, the outer support
element is a cemented tungsten carbide with a cobalt content ranging from
6 to 13 percent.

[0063] In other embodiments, the outer support element may be formed of
alloy steels, nickel-based alloys, and cobalt-based alloys. One of
ordinary skill in the art would also recognize that cutting element
components may be coated with a hardfacing material for increased erosion
protection. Such coatings may be applied by various techniques known in
the art such as, for example, detonation gun (d-gun) and spray-and-fuse
techniques.

[0064] Referring again to FIG. 2A, as the inner rotatable cutting element
210 is only partially disposed in and/or surrounded by the outer support
element 220, at least a portion of the inner rotatable cutting element
210 may be referred to as an "exposed portion" 216 of the inner rotatable
cutting element 210. Depending on the thickness of the exposed portion
216, exposed portion 216 may include at least a portion of the cutting
face 212 or the cutting face 212 and a portion of the substrate 214. As
shown in FIG. 2, exposed portion 216 includes cutting face 212 and a
portion of substrate 214. However, one of ordinary skill in the art would
recognize that while the exposed portion 216 is shown as being constant
across the entire diameter or width of the inner rotatable cutting
element 210, in the embodiment shown in FIG. 2, depending on the geometry
of the cutting element components, the exposed portion 216 of the inner
rotatable cutting element 210 may vary, as demonstrated by some of the
figures described below.

[0065] In a particular embodiment, the cutting face of the inner rotatable
cutting element has a thickness of at least 0.050 inches. However, one of
ordinary skill in the art would recognize that depending on the geometry
and size of the cutting structure, other thicknesses may be appropriate.

[0066] In another embodiment, the inner rotatable cutting element may have
a non-planar interface between the substrate and the cutting face. A
non-planar interface between the substrate and cutting face increases the
surface area of a substrate, thus may improve the bonding of the cutting
face to the substrate. In addition, the non-planar interfaces may
increase the resistance to shear stress that often results in
delamination of the diamond tables, for example.

[0067] One example of a non-planar interface between a carbide substrate
and a diamond layer is described, for example, in U.S. Pat. No.
5,662,720, wherein an "egg-carton" shape is formed into the substrate by
a suitable cutting, etching, or molding process. Other non-planar
interfaces may also be used including, for example, the interface
described in U.S. Pat. No. 5,494,477. According to one embodiment of the
present disclosure, a cutting face is deposited onto the substrate having
a non-planar surface.

[0068] Referring to FIG. 3A-B, a cutting element having a non-planar
interface is shown. As shown in this embodiment, cutting element 300
includes an inner rotatable (dynamic) cutting element 310 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 320. Outer support element 320 includes a bottom portion
322 and a side portion 324. Inner rotatable cutting element 310,
partially disposed within the cavity defined by the bottom portion 322
and side portion 324, includes a cutting face 312 portion disposed on an
upper surface 318 of substrate 314. As shown in FIG. 3A-B, upper surface
318 of substrate 314 is non-planar, creating a non-planar interface
between substrate 314 and 312.

[0069] The inner rotatable cutting element may be retained in the outer
support element by a variety of mechanisms, including for example, ball
bearings, pins, and mechanical interlocking. In various embodiments, a
single retention system may be used, while, alternatively, in other
embodiments, multiple retention systems may be used

[0070] Referring again to FIGS. 2A-3B, cutting elements having a ball
bearing retention system are shown. As shown in these embodiments, inner
rotatable cutting element 210, 310 and outer support element 220, 320
include substantially aligned/matching grooves 213, 313 and 223, 323 in
the side surface of the substrate 214, 314 and inner surface of the side
portion 224, 324, respectively. Occupying the space defined by grooves
213, 313 and 223, 323, are retention balls (i.e., ball bearings) 230, 330
to assist in retaining inner rotatable cutting element 210, 310 in outer
support element 220, 320. Balls may be inserted through pinhole 227, 327
in side portion 224, 324. In such an embodiment, following assembly of
the cutting element 200, 300, pinhole 227, 327 may be sealed with a pin
or plug 232, 332 or any other material capable of filling pinhole 227,
327 without impairing the function of retention balls/bearings 230, 330.
In alternative embodiments, cutting element 200, 300 may be formed from
multiple pieces as described above such that pinhole 227, 327 and plug
232, 332 are not required.

[0071] Balls 230, 330 may be made any material (e.g., steel or carbides)
capable of withstanding compressive forces acting thereupon while cutting
element 200, 300 engages the formation. In a particular embodiment the
balls may be formed of tungsten carbide or silicon carbide. If tungsten
carbide balls are used, it may be preferable to use a cemented tungsten
carbide composition varying from that of the outer support element and/or
substrate. Balls 230, 330 may be of any size and of which may be variable
to change the rotational speed of inner rotatable cutting element 210,
310. In certain embodiments, the rotatable speed of dynamic portion 210,
310 may be between one and five rotations per minute so that the surface
of cutting face 212, 312 may remain sharp without compromising the
integrity of cutting element 200, 300.

[0072] Referring again to FIG. 4, a cutting element having a pin retention
system is shown. As shown in this embodiment, cutting element 400
includes an inner rotatable (dynamic) cutting element 410 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 420. Outer support element 420 includes a bottom portion
422 and a side portion 424. Inner rotatable cutting element 410,
partially disposed within the cavity defined by the bottom portion 422
and side portion 424, includes a cutting face 412 portion disposed on an
upper surface of substrate 414. Further, inner rotatable cutting element
410 includes a groove 413 in the side surface of substrate 414.
Substantially aligned with the groove 413 is a pin 430 extending from the
inner surface of side portion 424. Pin 430 extends radially inward from
side portion 424 into the space defined by groove 413 to retain inner
cutting element 410 in outer support element 510.

[0073] Referring to FIGS. 5A-B, a cutting element having a mechanical
interlocking retention system is shown. As shown in this embodiment,
cutting element 500 includes an inner rotatable (dynamic) cutting element
510 which is partially disposed in and thus, partially surrounded by an
outer support (static) element 520. Outer support element 520 includes a
bottom portion 522, a side portion 524, and a top portion 526. Inner
rotatable cutting element 510 includes a cutting face 512 portion
disposed on an upper surface of substrate 514. Inner rotatable cutting
element is disposed within the cavity defined by the bottom portion 522,
side portion 524, and top portion 526. Due to the structural nature of
this embodiment, inner rotatable cutting element is mechanically retained
in the outer support element 520 cavity by bottom portion 522, side
portion 524, and top portion 526. As shown in FIG. 5, top portion 526
extends partially over the upper surface of cutting face 512 so as to
retain inner rotatable cutting element 510 and also allow for cutting of
a formation by the inner rotatable cutting element 510, and specifically,
cutting face 512.

[0074] Referring to FIGS. 6A-B, a cutting element having another
mechanical interlocking retention system is shown. As shown in this
embodiment, cutting element 600 includes an inner rotatable (dynamic)
cutting element 610 which is partially disposed in, and thus, partially
surrounded by an outer support (static) element 620. Outer support
element 620 includes a bottom portion 622 and a side portion 624. Inner
rotatable cutting element 610, partially disposed within the cavity
defined by the bottom portion 622 and side portion 624, includes a
cutting face 612 portion disposed on an upper surface of substrate 614.
Further, inner rotatable cutting element 610 and outer support element
620 include substantially aligned/matching groove 613 and protrusion 623
in the side surface of the substrate 614 and inner surface of the side
portion 624, respectively. As non-planar mating surfaces, groove 613 and
protrusion 623 assist in retaining inner rotatable cutting element 610 in
outer support element 620. One of skill in the art would recognize that
other non-planar, mating surfaces in substrate 614 and side portion 624
may be formed to retain inner rotatable cutting element 610 in outer
support element 620. For example, substrate 614 may include a protrusion
that may be substantially aligned with a groove in side portion 624.

[0075] In various embodiments including, for example, those shown in FIGS.
2A-B and 4 above, the cutting elements disclosed herein may include a
seal between the inner rotatable cutting element and the outer support
element. As shown in FIGS. 2A-B and 4, a seal or sealing element 240, 440
is disposed between inner rotatable cutting element 210, 410 and outer
support element 220, 420, specifically, on the conical surface of the
inner rotatable cutting element 210, 410. Sealing element 240, 440 may be
provided, in one embodiment, to reduce contact between the inner
rotatable cutting element 210, 410 and the outer support element 220, 420
and may be made from any number of materials (e.g., rubbers, elastomers,
and polymers) known to one of ordinary skill in the art. As such, sealing
element 240, 440 may reduce heat generated by friction as inner rotatable
cutting element 210, 410 rotates within outer support element 220, 420.
Further, sealing element 240, 440 may also act to reduce galling or
seizure of bearings 230 or pin 430 due to mud infusion or compaction of
drill cuttings. In optional embodiments, grease, or any other friction
reducing material may be added in the seal groove between inner rotatable
cutting element 210, 410 and outer support element 220, 420. Such
material may prevent the build-up of heat between the components, thereby
extending the life of cutting element 200, 400.

[0076] Referring to FIG. 7, a cutting element with alternative seal system
is shown. As shown in this embodiment, cutting element 700 includes an
inner rotatable (dynamic) cutting element 710 which is partially disposed
in, and thus, partially surrounded by an outer support (static) element
720. Outer support element 720 includes a bottom portion 722 and a side
portion 724. Inner rotatable cutting element 710, partially disposed
within the cavity defined by the bottom portion 722 and side portion 724,
includes a cutting face 712 portion disposed on an upper surface of
substrate 714. Sealing system 740 is disposed between inner rotatable
cutting element 710 and outer support element 720, specifically, as shown
in FIG. 7, between an upper surface 729 of outer support element 720 and
a lower surface 719 of exposed portion 716 of inner rotatable cutting
element 710. Sealing system 740 is a two component system and includes
metal seal component 742 and an o-ring component 744.

[0077] In one embodiment, the bearing surfaces of the cutting elements
disclosed herein may be enhanced to promote rotation of the inner
rotatable cutting element in the outer support element. Bearing surface
enhancements may be incorporated on a portion of either or both of the
inner rotatable cutting element bearing surface and outer support element
bearing surface. In a particular embodiment, at least a portion of one of
the bearing surfaces may include a diamond bearing surface. According to
the present disclosed, a diamond bearing surface may include discrete
segments of diamond in some embodiments and a continuous segment in other
embodiments. Bearing surfaces that may be used in the cutting elements
disclosed herein may include diamond bearing surfaces, such as those
disclosed in U.S. Pat. Nos. 4,756,631 and 4,738,322, assigned to the
present assignee and incorporated herein by reference in its entirety.

[0078] Referring to FIG. 8A-B, a cutting element having a diamond bearing
surface is shown. As shown in this embodiment, cutting element 800
includes an inner rotatable (dynamic) cutting element 810 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 820. Outer support element 820 includes a bottom portion
822, a side portion 824, and a top portion 826. Inner rotatable cutting
element 810 includes a cutting face 812 portion disposed on an upper
surface of substrate 814. Inner rotatable cutting element is disposed
within the cavity defined by the bottom portion 822, side portion 824,
and top portion 826. Due to the structural nature of this embodiment,
inner rotatable cutting element is mechanically retained in the outer
support element 820 cavity by bottom portion 822, side portion 824, and
top portion 826. As shown in FIGS. 8A-B, top portion 826 extends
partially over the upper surface of cutting face 812 so as to retain
inner rotatable cutting element 810 and also allow for cutting of a
formation by the inner rotatable cutting element 810, and specifically,
cutting face 812. Side surface of substrate 814 includes continuous,
circumferential diamond bearing surfaces 850. Similar to FIGS. 8A-B, the
embodiment shown in FIGS. 9A-B includes diamond bearing surfaces 950 on
substrate 914; however, diamond bearing surfaces 950 are discrete
segments of diamond along the circumferential side surface of substrate
914. As shown in FIGS. 10A-B, discrete segments of diamond bearing
surfaces 1050 are included on the side surface of substrate 1014 and
inner surface of side portion 1024. While this illustrated embodiment
shows discrete

[0079] Thus, in some embodiments, diamond-on-diamond bearing surfaces may
be provided. This may be achieved by using diamond enhanced bearing
surfaces on both the inner rotatable cutting element and outer support
element, or alternatively, the substrate may be formed of diamond and
diamond enhanced bearing surfaces may be provided on the outer support
element. In other embodiments, diamond-on-carbide bearing surfaces may be
used, where diamond bearing surfaces may be included on one of the
substrate or the outer support element, where carbide comprises the other
component.

[0080] To further enhance rotation of the inner rotatable cutting element,
the bottom mating surfaces of the inner rotatable cutting element and
outer support element may be varied. For example, ball bearings may be
provided between the two components or, alternatively, one of the
surfaces may be contain and/or be formed of diamond.

[0081] Referring to FIGS. 8A-10B, cutting elements according to one
embodiment of the present disclosure is shown. As shown in these
embodiments, inner rotatable cutting element 810, 910, 1010 includes a
lower diamond face 860, 960, 1060 on the lower surface of substrate 814,
914, 1014 such that bottom portion 822, 922, 1022 of outer support
element 820, 920, 1020 contacts inner rotatable cutting element 810, 910,
1010 at lower diamond face 860, 960, 1060. In alternative embodiments,
diamond may be include in discrete regions on the lower surface of
substrate 814, 914, 1014 may or in discrete regions or a layer on inner
surface of bottom portion 822, 922, 1022 of outer support element 820,
920, 1020.

[0082] Another embodiment of a diamond enhanced bearing surface is shown
in FIG. 11. Referring to FIG. 11, a cutting element 1100 includes an
inner rotatable (dynamic) cutting element 1110 which is partially
disposed in, and thus, partially surrounded by an outer support (static)
element 1120. Outer support element 1120 includes a bottom portion 1122
and a side portion 1124. Inner rotatable cutting element 1110 includes a
cutting face 1112 portion disposed on an upper surface of substrate 1114.
Inner rotatable cutting element is disposed within the cavity defined by
the bottom portion 1122 and side portion 1124. At the upper surface of
side portion 1124 of outer support element 1120, a portion of inner
rotatable cutting element 1110 is juxtaposed thereto, creating a bearing
surface therebetween. As shown in FIG. 11, a circumferential diamond
layer 1155 may be disposed on the upper bearing surface of side portion
1124 and contact the inner rotatable cutting element 1110. The diamond
layer 1155 may also acts as a cutting mechanism and/or to provide lateral
protection to the inner rotatable cutting element 1110 when the bit is
subjected to vibration.

[0083] Referring again to FIGS. 3A-B, a cutting element according to
another embodiment of the present disclosure is shown. As shown in this
embodiment, inner rotatable cutting element 310 and outer support element
320 include substantially aligned/matching grooves 315 and 325 in the
lower surface of the substrate 314 and inner surface of the bottom
portion 322, respectively. Occupying the space defined by grooves 315 and
325, are ball bearings 365 to assist in rotation of inner rotatable
cutting element 310 in outer support element 320.

[0084] In another embodiment, at least a portion of at least one of the
bearing surfaces may be surface treated for optimizing the rotation of
the inner rotatable cutting element in the inner support element. Surface
treatments suitable for the cutting elements of the present disclosure
include addition of a lubricant, applied coatings and surface finishing,
for example. In a particular embodiment, a bearing surface may undergo
surface finishing such that the surface has a mean roughness of less than
about 125 μ-inch Ra, and less than about 32 μ-inch Ra in another
embodiment. In another particular embodiment, a bearing surface may be
coated with a lubricious material to facilitate rotation of the inner
rotatable cutting element and/or to reduce friction and galling between
the inner rotatable cutting element and the outer support element. In a
particular embodiment, a bearing surface may be coated with a carbide,
nitride, and/or oxide of various metals that may be applied by PVD, CVD
or any other deposition techniques known in the art that facilitate
bonding to the substrate or base material. In another embodiment, a
floating bearing may be included between the bearing surfaces to
facilitate rotation. Incorporation of a friction reducing material, such
as a grease or lubricant, may allow the surfaces of the inner rotatable
cutting element and the outer support element to rotate and contract one
another, but result in only minimal heat generation therefrom.

[0085] In another embodiment, surface alterations may be included on the
working surfaces of the cutting face, the substrate, and/or an inner hole
of the inner rotatable cutting element. Surface alterations may be
included in the cutting elements of the present disclosure to enhance
rotation through hydraulic interactions or physical interactions with the
formation. In various embodiments, surface alterations may be etched or
machined into the various components, or alternatively formed during
sintering or formation of the component, and in some particular
embodiments, may have a depth ranging from 0.001 to 0.050 inches. One of
ordinary skill in the art would recognize the surface alterations may
take any geometric or non-geometric shape on any portion of the inner
rotatable cutting element and may be formed in a symmetric or asymmetric
manner. Further, depending on the size of the cutting elements, it may be
preferable to vary the depth of the surface alterations.

[0086] Referring to FIGS. 12A-B, a cutting element having a non-planar
cutting face is shown. As shown in this embodiment, cutting element 1200
includes an inner rotatable (dynamic) cutting element 1210 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 1220. Outer support element 1220 includes a bottom
portion 1222 and a side portion 1224. Inner rotatable cutting element
1210 includes a cutting face 1212 portion disposed on an upper surface of
substrate 1214. Inner rotatable cutting element is disposed within the
cavity defined by the bottom portion 1222 and side portion 1224. Cutting
face 1212 includes surface alterations 1272 on its top surface. As shown
in FIG. 12, surface alterations 1272 are in a serrated manner extending
radially from a midpoint on the top surface to the cutting edge 1270.
While the surface alterations 1272 shown in FIG. 12 are in a serrated
manner with generally sharp edges, it is within the scope of the present
disclosure that such surface features used in the cutting elements of the
present disclosure may take on a variety of forms (i.e., geometric
shapes, waves, sharp, smooth, etc.).

[0087] Referring to FIG. 13, another cutting element having a non-planar
cutting face is shown. As shown in this embodiment, cutting element 1300
includes an inner rotatable (dynamic) cutting element 1310 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 1320. Outer support element 1320 includes a bottom
portion (now shown) and a side portion 1324. Inner rotatable cutting
element 1310 includes a cutting face 1312 portion disposed on an upper
surface of substrate (not shown). Inner rotatable cutting element is
disposed within the cavity defined by the bottom portion (not shown) and
side portion 1324. Cutting face 1312 includes surface alterations 1374 on
its top surface and side surface, collectively, the working surface of
cutting face 1312. As shown in FIG. 13, surface alterations 1374 are in a
serrated manner extending radially from a midpoint on the top surface
over the cutting edge 1370 onto the side surface.

[0088] Referring to FIG. 14, a cutting element having a non-planar cutting
face and substrate is shown. As shown in this embodiment, cutting element
1400 includes an inner rotatable (dynamic) cutting element 1410 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 1420. Outer support element 1420 includes a bottom
portion (not shown), a side portion 1424, and top portion 1426. Inner
rotatable cutting element 1410 includes a cutting face 1412 portion
disposed on an upper surface of substrate 1414. Inner rotatable cutting
element is disposed within the cavity defined by the bottom portion (not
shown), side portion 1424, and top portion 1426. Cutting face 1412
includes surface alterations 1472 on its top surface. As shown in FIG.
14, surface alterations 1472 are in a serrated manner extending radially
from a midpoint on the top surface to the cutting edge 1470.
Additionally, the side surface of substrate 1414 includes surface
alterations 1476.

[0089] Referring to FIG. 15, a cutting element having a non-planar surface
thereon is shown. As shown in this embodiment, cutting element 1500
includes an inner rotatable (dynamic) cutting element 1510 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 1520. Outer support element 1520 includes a bottom
portion 1522 and a side portion 1524. Inner rotatable cutting element
1510 includes a cutting face 1512 portion disposed on an upper surface of
substrate 1514. Inner rotatable cutting element 1510 is disposed within
the cavity defined by the bottom portion 1522 and side portion 1524. An
internal bore 1580 extends through inner rotatable cutting element 1510
through the bottom portion 1522 of outer support element 1520. A passage
(not shown) may connect internal bore 1580 to a fluid conduit on, for
example, a drill bit surface, a blade, or a drill bit assembly.

[0090] Internal bore 1580 may be formed with surface alterations or
geometrically shaped edges (e.g., rifling and/or twisting) (not shown) to
direct the flow of fluid therethrough. Such fluid direction may give the
inner rotatable cutting element 1510 a greater likelihood of continuous
motion in one direction. In this embodiment, a fluid may be directed
through passage (not shown) into internal bore 1580, therein generating a
rolling force. The fluid may exit cutting element 1500 in a variety of
ways, including through spacing (not shown) between inner rotatable
cutting element 1510 and outer support element 1520 or through a second
internal passage (not shown) and be directed back into the fluid conduit.

[0091] While the above embodiments describe surface alterations formed,
for example, by etching or machining, it is also within the scope of the
present disclosure that the cutting element includes a non-planar cutting
face that may be achieved through protrusions from the face. Non-planar
cutting faces may also be achieved through the use of shaped cutting
faces in the inner rotatable cutting element. For example, shaped cutting
faces suitable for use in the cutting elements of the present disclosure
may include domed or rounded tops and saddle shapes.

[0092] Referring to FIGS. 16A-B, a cutting element having a non-planar
cutting face is shown. As shown in this embodiment, cutting element 1600
includes an inner rotatable (dynamic) cutting element 1610 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 1620. Outer support element 1620 includes a bottom
portion 1622 and a side portion 1624. Inner rotatable cutting element
1610 includes a cutting face 1612 portion disposed on an upper surface of
substrate 1614. Inner rotatable cutting element is disposed within the
cavity defined by the bottom portion 1622 and side portion 1624. As shown
in FIGS. 16A-B, cutting face 1612 is dome shaped.

[0093] Further, the types of bearing surfaces between the inner rotatable
cutting element and outer support elements present in a particular
cutting element may vary. Among the types of bearing surfaces that may be
present in the cutting elements of the present disclosure include conical
bearing surfaces, radial bearing surfaces, and axial bearing surfaces.

[0094] In one embodiment, the inner rotatable cutting element may of a
generally frusto-conical shape within an outer support element having a
substantially mating shape, such that the inner rotatable cutting element
and outer support element have conical bearing surfaces therebetween.
Referring to FIGS. 2A-B, such an embodiment with conical bearing surfaces
is shown. As shown in this embodiment, conical bearing surfaces 292
between the inner rotatable cutting element 210 and outer support element
220 may serve to take a large portion of the thrust from the rotating
inner rotatable cutting element 210 during operation as it interacts with
a formation. Further, in applications needing a more robust cutting
element, a conical bearing surface may provide a larger area for the
applied load. The embodiment shown in FIG. 2A-B also shows a radial
bearing surface 294 and an axial bearing surface 296.

[0095] Referring to FIGS. 12A-B, a cutting element according to another
embodiment is shown. As shown in this embodiment, the inner rotatable
cutting element 1210 has a generally cylindrical shape with the side
portion 1224 of outer support element having a generally annular or
mating shape, such that the inner rotatable cutting element 1210 and
outer support element 1220 having a radial bearing surface 1294
therebetween.

[0096] Referring to FIGS. 17A-B, a cutting element according to another
embodiment is shown. As shown in this embodiment, cutting element 1700
includes an inner rotatable (dynamic) cutting element 1710 which is
partially disposed in, and thus, partially surrounded by an outer support
(static) element 1720. Outer support element 1720 includes a bottom
portion 1722 and a side portion 1724. Inner rotatable cutting element
1710 includes a cutting face 1712 portion disposed on an upper surface of
substrate 1714. At the upper surface of side portion 1724 of outer
support element 1720, a portion of inner rotatable cutting element 1710
is juxtaposed thereto, creating an axial bearing surface 1796
therebetween. Cutting element 1700 also has a radial bearing surface 1794
between inner rotatable cutting element 1710 and side portion 1724 of
outer support element 1720.

[0097] In one further embodiment, a distance between an upper surface of
the cutting face and a bearing surface may be varied to reduce or prevent
fracture of the inner rotatable cutting elements due to excessive bending
stresses encountered during drilling. In the embodiment shown in FIG. 2,
the distance between the upper surface of the cutting face 212 and the
axial bearing surface 296 and/or conical bearing surface 292 is
equivalent to the exposed portion 216. However, in the embodiment shown
in FIG. 12, because the side portion 1224 (and hence the radial bearing
surface 1294) extends to the upper surface of cutting face 1212, the
distance between the upper surface of cutting face 1212 and radial
bearing surface 1924 is zero. In various embodiments, the shape of the
cutting element components may be designed such that the distance between
the upper surface of the cutting face and a bearing surface may range
from 0 to about 0.300 inches.

[0098] Referring to FIG. 18, a cutting element according to another
embodiment is shown. As shown in this embodiment, cutting element 1800
includes an inner rotatable (dynamic) cutting element 1810 which is
partially disposed in, and thus, partially surrounded by an outer support
(static element) 1820. Outer support element 1820 includes a bottom
portion 1822 and a side portion 1824. Inner rotatable cutting element
1810 includes a cutting face 1812 portion disposed on an upper surface of
substrate 1814. As shown in this embodiment, outer support element 1820
is integral with a bit body (not shown). In alternative embodiments,
outer support element 1820 may be a discrete element or outer support
element 1820 may include for example, a discrete side portion 1824 and a
bottom portion integral with the bit. As also shown in this embodiment,
outer support element 1820 also includes a inner shaft portion 1828
extending from bottom portion 1822 into substrate 1814 of inner rotatable
cutting element 1810 such that when inner rotatable cutting element 1810
rotates, it rotates within side portion 1824 and about inner shaft
portion 1828 of outer support element 1820. Retention balls (i.e., ball
bearings) 1830 are disposed in grooves 1813, 1823 in the inner rotatable
cutting element 1810 and outer support element 1820, respectively, and
assist in retaining inner rotatable cutting element 1810 within outer
support element 1820. A seal 1840 is disposed between a lower surface of
substrate 1814 and bottom portion 1822. As shown in the illustrated
embodiment, the cutting element includes an outer cylindrical bearing
surface 1894 between side portion 1824 and substrate 1814 and an inner
cylindrical bearing surface 1898 between inner shaft portion 1828 and
substrate 1814.

[0099] Referring to FIG. 19, a cutting element according to another
embodiment is shown. As shown in this embodiment, cutting element 1900
includes an inner rotatable (dynamic) cutting element 1910 which is
partially disposed in, and thus, partially surrounded by an outer support
(static element) 1920. Outer support element 1920 includes a bottom
portion 1922 and a side portion 1924. Inner rotatable cutting element
1910 includes a cutting face 1912 portion disposed on an upper surface of
substrate 1914. As shown in this embodiment, outer support element 1920
is integral with a bit body (not shown). In alternative embodiments,
outer support element 1920 may be a discrete element. As also shown in
this embodiment, outer support element 1920 also includes a inner shaft
portion 1928 threadedly attached to and extending from bottom portion
1922 into substrate 1914 of inner rotatable cutting element 1910 such
that when inner rotatable cutting element 1910 rotates, it rotates within
side portion 1924 and about inner shaft portion 1928 of outer support
element 1920. In alternative embodiments, inner shaft portion 1928 may be
integral with bottom portion 1922. Upper end of inner shaft portion 1928
extends partially over the cutting face 1912 of the inner rotatable
cutting element 1910 to assist in retaining the inner rotatable cutting
element 1910 within the outer support element 1920.

[0100] As shown in the various illustrated above, the inner rotatable
cutting element and outer support cutting element may take the form of a
variety of shapes/geometries. Depending on the shapes of the components,
different bearings surfaces, or combinations thereof may exist between
the inner rotatable cutting element and outer support element. However,
one of ordinary skill in the art would recognize that permutations in the
shapes may exist and any particular geometric forms should not be
considered a limitation on the scope of the cutting elements disclosed
herein.

[0101] Further, one of ordinary skill in the art would also appreciate
that any of the design modifications as described above, including, for
example, side rake, back rake, variations in geometry, surface
alteration/etching, seals, bearings, material compositions, etc, may be
included in various combinations not limited to those described above in
the cutting elements of the present disclosure.

[0102] The cutting elements of the present disclosure may be incorporated
in various types of cutting tools, including for example, as cutters in
fixed cutter bits or as inserts in roller cone bits. Bits having the
cutting elements of the present disclosure may include a single rotatable
cutting element with the remaining cutting elements being conventional
cutting elements, all cutting elements being rotatable, or any
combination therebetween of rotatable and conventional cutting elements.

[0103] In some embodiments, the placement of the cutting elements on the
blade of a fixed cutter bit or cone of a roller cone bit may be selected
such that the rotatable cutting elements are placed in areas experiencing
the greatest wear. For example, in a particular embodiment, rotatable
cutting elements may be placed on the shoulder or nose area of a fixed
cutter bit. Additionally, one of ordinary skill in the art would
recognize that there exists no limitation on the sizes of the cutting
elements of the present disclosure. For example, in various embodiments,
the cutting elements may be formed in sizes including, but not limited
to, 9 mm, 13 mm, 16 mm, and 19 mm.

[0104] Referring now to FIG. 20, a cutting element 2000 disposed on a
blade 2002, in accordance with an embodiment of the present disclosure,
is shown. In this embodiment, cutting element 2000 includes an inner
rotatable cutting element 2010 partially disposed in outer support
element 2020. To vary the cutting action and potentially change the
cutting efficiency and rotation, one of ordinary skill in the art should
understand that the back rake (i.e., a vertical orientation) and the side
rake (i.e., a lateral orientation) of the cutting element 2000 may be
adjusted.

[0105] Referring to FIG. 21, a cutting structure profile of a bit
according to one embodiment is shown. As shown in this embodiment,
cutters 2100 positioned on a blade 2102 may have side rake or back rake.
Side rake is defined as the angle between the cutting face 2105 and the
radial plane of the bit (x-z plane). When viewed along the z-axis, a
negative side rake results from counterclockwise rotation of the cutter
2100, and a positive side rake, from clockwise rotation. Back rake is
defined as the angle subtended between the cutting face 2105 of the
cutter 2100 and a line parallel to the longitudinal axis 2107 of the bit.
In one embodiment, a cutter may have a side rake ranging from 0 to ±45
degrees. In another embodiment, a cutter may have a back rake ranging
from about 5 to 35 degrees.

[0106] A cutter may be positioned on a blade with a selected back rake to
assist in removing drill cuttings and increasing rate of penetration. A
cutter disposed on a drill bit with side rake may be forced forward in a
radial and tangential direction when the bit rotates. In some embodiments
because the radial direction may assist the movement of inner rotatable
cutting element relative to outer support element, such rotation may
allow greater drill cuttings removal and provide an improved rate of
penetration. One of ordinary skill in the art will realize that any back
rake and side rake combination may be used with the cutting elements of
the present disclosure to enhance rotatability and/or improve drilling
efficiency.

[0107] As a cutting element contacts formation, the rotating motion of the
cutting element may be continuous or discontinuous. For example, when the
cutting element is mounted with a determined side rake and/or back rake,
the cutting force may be generally pointed in one direction. Providing a
directional cutting force may allow the cutting element to have a
continuous rotating motion, further enhancing drilling efficiency.

[0108] In alternate embodiments, cutting elements may be disposed in drill
bits that do not incorporate back rake and/or side rake. When the cutting
element is disposed on a drill bit with substantially zero degrees of
side rake and/or back rake, the cutting force may be random instead of
pointing in one general direction. The random forces may cause the
cutting element to have a discontinuous rotating motion. Generally, such
a discontinuous motion may not provide the most efficient drilling
condition, however, in certain embodiments, it may be beneficial to allow
substantially the entire cutting surface of the insert to contact the
formation in a relatively even manner. In such an embodiment, alternative
inner rotatable cutting element and/or cutting surface designs may be
used to further exploit the benefits of rotatable cutting elements.

[0109] The cutting elements of the present disclosure may be attached to
or mounted on a drill bit by a variety of mechanisms, including but not
limited to conventional attachment or brazing techniques in a cutter
pocket. One alternative mounting technique that may be suitable for the
cutting elements of the present disclosure is shown in FIG. 22. As shown
in this embodiment, cutting elements 2200 are mounted in an assembly
2201, which may be mounted on a bit body (not shown) by means such as
mechanical, brazing, or combinations thereof. It is also within the scope
of the present disclosure that in some embodiments, an inner rotatable
cutting element may be mounted on the bit directly such that the bit body
acts as the outer support element, i.e., by inserting the inner rotatable
cutting element into a hole that may be subsequently blocked to retain
the inner rotatable cutting element within.

[0110] Advantageously, embodiments disclosed herein may provide for at
least one of the following. Cutting elements that include a rotatable
cutting portion may avoid the high temperatures generated by typical
fixed cutters. Because the cutting surface of prior art cutting elements
is constantly contacting formation, heat may build-up that may cause
failure of the cutting element due to fracture. Embodiments in accordance
with the present invention may avoid this heat build-up as the edge
contacting the formation changes. The lower temperatures at the edge of
the cutting elements may decrease fracture potential, thereby extending
the functional life of the cutting element. By decreasing the thermal and
mechanical load experienced by the cutting surface of the cutting
element, cutting element life may be increase, thereby allowing more
efficient drilling.

[0111] Further, rotation of a rotatable portion of the cutting element may
allow a cutting surface to cut formation using the entire outer edge of
the cutting surface, rather than the same section of the outer edge, as
provided by the prior art. The entire edge of the cutting element may
contact the formation, generating more uniform cutting element edge wear,
thereby preventing for formation of a local wear flat area. Because the
edge wear is more uniform, the cutting element may not wear as quickly,
thereby having a longer downhole life, and thus increasing the overall
efficiency of the drilling operation.

[0112] Additionally, because the edge of the cutting element contacting
the formation changes as the rotatable cutting portion of the cutting
element rotates, the cutting edge may remain sharp. The sharp cutting
edge may increase the rate of penetration while drilling formation,
thereby increasing the efficiency of the drilling operation. Further, as
the rotatable portion of the cutting element rotates, a hydraulic force
may be applied to the cutting surface to cool and clean the surface of
the cutting element.

[0113] Some embodiments may protect the cutting surface of a cutting
element from side impact forces, thereby preventing premature cutting
element fracture and subsequent failure. Still other embodiments may use
a diamond table cutting surface as a bearing surface to reduce friction
and provide extended wear life. As wear life of the cutting element
embodiments increase, the potential of cutting element failure decreases.
As such, a longer effective cutting element life may provide a higher
rate of penetration, and ultimately result in a more efficient drilling
operation.

[0114] While the invention has been described with respect to a limited
number of embodiments, those skilled in the art, having benefit of this
disclosure, will appreciate that other embodiments can be devised which
do not depart from the scope of the invention as disclosed herein.
Accordingly, the scope of the invention should be limited only by the
attached claims.